Optic tectal superficial interneurons detect motion in larval zebrafish

Detection of moving objects is an essential skill for animals to hunt prey, recognize conspecifics and avoid predators. The zebrafish, as a vertebrate model, primarily uses its elaborate visual system to distinguish moving objects against background scenes. The optic tectum (OT) receives and integrates inputs from various types of retinal ganglion cells (RGCs), including direction-selective (DS) RGCs and size-selective RGCs, and is required for both prey capture and predator avoidance. However, it remains largely unknown how motion information is processed within the OT. Here we performed in vivo whole-cell recording and calcium imaging to investigate the role of superficial interneurons (SINs), a specific type of optic tectal neurons, in motion detection of larval zebrafish. SINs mainly receive excitatory synaptic inputs, exhibit transient ON- or OFF-type of responses evoked by light flashes, and possess a large receptive field (RF). One fifth of SINs are DS and classified into two subsets with separate preferred directions. Furthermore, SINs show size-dependent responses to moving dots. They are efficiently activated by moving objects but not static ones, capable of showing sustained responses to moving objects and having less visual adaptation than periventricular neurons (PVNs), the principal tectal cells. Behaviorally, ablation of SINs impairs prey capture, which requires local motion detection, but not global looming-evoked escape. Finally, starvation enhances the gain of SINs' motion responses while maintaining their size tuning and DS. These results indicate that SINs serve as a motion detector for sensing and localizing sized moving objects in the visual field.

THE EFFECTS OF STIMULATING OPTIC TECTUM ON THE SPINAL ACTIVITY IN BULLFROG / 西安交通大学学报(医学版)

By using dorsal root patientials (DRP) and ventral root patientials (VRP) as in dexes, the effects of descending volleys originating from the optic tectum on spinal activity were observed in bullfrogs. The experimental results obtained were as follows; 1.DRP was evoked by stimulation of the optic rectum. 2. VRP evoked by stimulation of the siatic nerve comsisted of two components. The early conponent was evoked chiefly by type Ⅰ and Ⅱ afferent fibers and also contributed by type Ⅲ fibers; the late one was evoked by type Ⅳ afferent fibers. 3. VRP evoked by stimulation of the siatic nerve was inhibited by stimulation of the optic tectum. The duration of inhibition of the early component was related to that of DRP. Thus, the results indicate that the optic tectum takes part in the centrifugal control of somatosensory afferent activity, affects the spinal reflex, and involves in the mechanism of analgesia by way of presynaptic inhibition.

NEURONAL PATHWAYS AND MORPHOLOGY OF ORIGINATING CELLS IN THE LACERTILIAN MIDBRAIN / 解剖学报

The present paper studies the neuronal pathways connecting the optic tectum(?)the nucleus profundus mesencephali(NPM)and the nucleus isthmi,and the morph-ology of their originating cells in Gekko gekko and Shinisaurus crocodilurus byusing horseradish peroxidase(HRP)tracing method.The results indicate that 1.There exist reciprocal topographic projections between the tectum and the nucleus.isthmi pars magnocellularis(Imc);2.The ipsilateral tecto-Imc projection originatesfrom cells mainly located in layer 7,which have piriform somata with radical den- drites;the ipsilateral Imc-tectal projection originates from piriform or polygonalneurons with a small dendritic field;3.Cells labeled in NPM following tectal injections are fusiform in shape,paler in color,whereas NPM cells labeled followingisthmic injections are numerous,whose thick dendrites often go up to the tectum(?)4.NPM injections label both tectal and isthmic cells.The former are mainly loca-ted within layer 7,while the latter are in Imc and Ipc.